Whooping sound?

[ak46champ]

OK I give up! It is hard to describe but I have what sounds like a whooping sound from the right side of the engine, Compressions on all cylinders hold good at 400psi +. No exhaust leak. Replaced 4 bad injectors. Good Oil pressure and good boost. Sound used to go away when engine got warm. Now it doesn't. I use Delo 400 Oil and the oil level is good. Local Diesel mechanic thinks its an injection pump. Another friend has the same sound in his and he replaced his injection pump and injectors with all new (He had other issues though, now he has no oil pressure, 155,000 miles) I on the other hand have just broke 100,000 on this one. He thinks its a lifter that is going bad by either bad cam lobe or sticking lifter.

Would appreciate any suggestions!

Thanks